Vehicles typically have an air filter that cleans outside air before the air is ingested into the engine to mix with fuel before combustion. Over time, the air filter becomes clogged with dust, dirt, and other debris, in particular if the vehicle travels on dirt roads. Symptoms of a dirty/clogged air filter may vary but often include a noticeable decrease in gas mileage. Other symptoms include potential ignition problems caused by fouled spark plugs. A dirty air filter prevents the necessary volume of clean air from reaching the engine, which affects the emission control systems of the vehicle, reducing air flow and causing a too rich air-fuel mixture which can foul the spark plugs. In addition, a too rich fuel mixture increases engine deposits.
Various approaches for diagnosing a dirty or clogged air filter have been proposed. For example, U.S. Pat. No. 5,606,311 discloses an intake air filter diagnostic routine that compares a pressure drop across the air filter to an expected pressure drop across the air filter for the given operating conditions. If the pressure drop is greater than the expected pressure drop, the air filter is determined to be clogged and an operator of the vehicle is notified.
However, the inventor herein has recognized an issue with the above approach. Monitoring the pressure drop across the air filter typically requires additional components, such as additional pressure sensors. In the example presented above, for example, the air filter is equipped with a switch assembly including two pressure switches each configured to switch states when a pressure difference acting on a flexible diaphragm of the switch assembly is above a respective threshold. The inclusion of such additional components increases the cost of the vehicle. Further, in boosted engine systems, the intake air pressure downstream of the air filter may not correlate with the intake manifold pressure. Thus, the pressure measurements provided by the existing intake manifold pressure sensor may not be useful in determining the pressure drop across the air filter.
Accordingly, the inventor herein has proposed an approach to at least partly address the above issues. In an example, a method for an engine coupled to an air filter and to a fuel tank includes indicating air filter clogging responsive to a measured fuel tank pressure during boosted engine operation. In this way, the existing fuel tank pressure sensor may be repurposed during boosted engine operation to detect air filter clogging. During boosted engine operation, vacuum may be generated between the air filter and an inlet of a compressor positioned downstream of the air filter, and the amount of vacuum produced depends on the level of clogging of the air filter (e.g., a clogged air filter will result in more vacuum being generated). The fuel tank pressure sensor may be fluidically coupled to the intake passage downstream of the air filter via a fuel vapor canister purge conduit during the boosted engine operation to expose the fuel tank pressure sensor to the vacuum downstream of the air filter. If the vacuum is greater than a threshold, for example, air filter clogging may be indicated and an operator may be notified to clear or replace the air filter. In doing so, a clogged air filter may be detected using existing vehicle components during normal engine operation, allowing the air filter to be replaced, if indicated, before a regularly scheduled maintenance of the vehicle, thereby improving fuel economy and reducing spark plug fouling.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.